1. Technical Field
The invention relates to precision measurement instruments, and to calipers with a movable jaw for measuring the dimensions of an object.
2. Description of the Related Art
Calipers utilize pairs of jaws for determining measurements. A first jaw is generally fixed at one end of a measurement scale while a second jaw is attached to a slider assembly that moves along the measurement scale. An outer dimension of an object may be measured by arranging the object between and against inner surfaces of the first and second jaws. An inner dimension of an object may be measured by arranging outer surfaces of the first and second jaws against the inner surfaces of the object (e.g. the walls of a hole). The slider assembly may be moved with a user's thumb, and a thumb wheel may be provided for improved control. One exemplary caliper utilizing a thumb wheel is described in U.S. Pat. No. 7,533,474, which is hereby incorporated herein by reference in its entirety.
For measuring the distance between the jaws of the caliper, electronic position encoders may be used, based on low-power inductive, position sensing technology for example. Such an encoder may comprise a readhead and a scale. The readhead may comprise a readhead sensor and readhead electronics. The readhead outputs signals that vary as a function of the position of the readhead sensor relative to the scale along a measuring axis. The scale may be affixed to an elongated scale member that includes a fixed first measuring jaw. The readhead is affixed to a slider assembly including the second measuring jaw, which is movable along the scale member. Measurements of the distance between the two measuring jaws may be determined based on the signals from the readhead.
Exemplary electronic calipers are disclosed in commonly assigned U.S. Pat. Nos. RE37490, 5,574,381, and 5,973,494, each of which is hereby incorporated by reference in its entirety. A prior art electronic caliper that is capable of measuring force is disclosed in U.S. Patent Publication No. 2003/0047009. As described in the '009 publication, one deficiency in the use of prior calipers is the variation in force applied by the measuring jaws and measurement differences which can occur as a result. Particularly when a soft object is measured, the measurement may be non-repeatable because one may apply either a higher force or lower force on the jaws of the caliper such that the soft object is “more compressed”, or“less compressed”. The '009 publication discloses a caliper that is capable of measuring both the size and force applied to an object, which may be analyzed to provide more repeatable measurements. However, the force sensing and indicating features of the caliper of the '009 publication may be considered “overkill” and/or too expensive and/or complex by many caliper users. A need exists for improving measurement force control and/or repeatability in a caliper in an economical, ergonomically convenient, repeatable, and intuitively understandable manner.